U.S. Pat. No. 4,028,582 to C. H. Anderson et al, issued June 7, 1977, entitled "Guided Beam Flat Display Device" describes a modular flat display device in which a relatively flat, evacuated envelope is divided into parallel channels by support walls extending between and substantially perpendicular to substantially parallel front and back walls of the envelope. Along each channel are three beam guides for guiding three parallel beams of electrons along the channel and for selectively deflecting the beams at selective points along the channel toward a phosphor screen on the front wall of the envelope. Between the beam guide and the phosphor screen are deflection electrodes which simultaneously deflect the three beams transversely across the channel so that all three beams transversely scan the entire portion of the screen which extends across the channel. The phosphor screen is made up of a sequence of triads of bodies of three different color emitting phosphors and each beam in the channel impinges on a different color phosphor. A shadow mask extends across the channel adjacent the screen and the beams pass through openings in the shadow mask.
A problem with the above modular flat display device is that the three beams in each channel follow substantially parallel paths as the beams are deflected across the channel. Thus, in order for each beam to scan the entire portion of the screen two of the beams must overscan onto the support wall at each side of the channel. This results in a relatively high peak beam current and a relatively high scan power for operating the display device.